How to sum a list of numbers in Emacs Lisp?

Question

This works:

(+ 1 2 3)
6

This doesn't work:

(+ '(1 2 3))

This works if 'cl-*' is loaded:

(reduce '+ '(1 2 3))
6

If reduce were always available I could write:

(defun sum (L)
  (reduce '+ L))

(sum '(1 2 3))
6

What is the best practice for defining functions such as sum?

Solution 1

(apply '+ '(1 2 3))

Solution 2

If you manipulate lists and write functional code in Emacs, install dash.el library. Then you could use its -sum function:

(-sum '(1 2 3 4 5)) ; => 15

Solution 3

Linearly recursive function (sum L)

;;
;; sum
;;
(defun sum(list)    
    (if (null list)
        0

        (+ 
            (first list) 
            (sum (rest list))
        )   
    )   
)